Irradiating the HeNe laser on a disc rotating at low speed, the speed of each location on the rotating surface
was measured by analyzing images captured by a high speed camera. The Doppler shift, which was generated when the
laser light was mixed with the Doppler-shifted light scattering signal generated at each position when the laser light was
irradiated on the rotating surface, was acquired by a high-speed camera to store in a memory. After performing FFT for
stored measurements of each location, the Doppler-shifted value was converted to the rotational speed. The maximum
measurable rotational speed was determined depending on a frame speed of the camera, and the speed distribution of
the rotating surface was measured.
A new laser Doppler velocimeter employing an RF-excited CO2 laser has been developed by using its photoacoustic effect. A change in the pressure of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as small as 50 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.
We stabilized a frequency and a power of RF excited CO2 laser to the centers of the Doppler broadened gain curves using a photoacoustic effect generated from the laser itself. The frequency stability is estimated to be better than of 5.4x10-8 and power variation is greatly improved to 9%. We suggest that this method can be applied for frequency and power stabilization of other kinds of RF excited laser, for example Xe and CO laser.
We stabilized the high voltage (HV) excited CO2 laser to the center of the gain curves using a photoacoustic effect generated from the laser itself. A commercial condenser microphone is located in the plasma free region. This detects pressure waves occurring in the plasma free region when laser radiation is absorbed. The signal from the microphone is used to control a feedback circuit to stabilize the frequency and power of the laser radiation. The frequency stability is estimated to be better then 3X10-8.
The prototype of He-Ne / He-Xe laser system for methane detection using differential absorption of radiation backscattered from topographic targets is described. Using radiation of the wavelengths 3.39 μm and 3.51 μm, the measurement of CH4 at the distance of 50 m was carried out. To increase the range and accuracy of measurement, the Cassegrain optics and lasers of higher power can be used. The lasers have four-channel construction structure and they are excited with RF current.
A new laser Doppler velocimeter employing a CO2 laser has been developed by using its photoacoustic effect. A change of the pressure of a laser discharge tube, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as much as 60 kHz was detected, and as well as a good linear relationship between the velocity and the Doppler frequency shift was obtained.
The prototype of the dual He-Ne/He-Xe laser system for gas detection using differential absorption of radiation backscattered from topographic targets is described. Both lasers were excited by dc discharge and for lengths of 80 cm we obtained the output power of about 10 mW. Using receiver optics with the diameter of 7 cm and thermocooled HgCdTe detector we can measure the presence of methane on the distance up to 50 m. The new solution is under construction. to increase the range of measurement, the Casseigrain optics with diameter of 25 cm is being prepared. Using the special construction of RF excited gas lasers with the output power of 40 mW, the measurement distance of 100 m is expected.
Four-channel structures in form of the second rank 2x2 matrix were investigated. For CO2 lasers we applied phase-locking techniques. He-Ne and He-Xe lasers were built as independent four-channels and optimized for their output power.
A new laser Doppler velocimeter employing a CO2 laser has been developed by using its photoacoustic effect. A change of the pressure of a laser discharge tube, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as much as 60 kHz was detected, and as well as a good linear relationship between the velocity and the Doppler frequency shift was obtained.
We stabilized an optical power of RE excited slab CO2 laser on the pick of the Doppler broadened gain curves using an optogalvanic effect generated from the laser itself. The power stability is greatly improved to 2.9 %. We suggest that this method can be applied for frequency and power stabilization of other kinds of RF excited laser, for example, Xe and Co laser.
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